1. Field of the Invention
Cross Compare for Systems running in a Multi Processor configuration, such as dual, 2-out-of-2, and triplicated, 2-out-of-3 configurations or some other multi-processor configuration.
2. Description of the Related Art
As CPU clock speeds have increased, and multi-processor architectures have become more common, processing performance capabilities have exceeded those of traditional RAM. One solution to this problem has been the adoption of multi-port RAM.
Multi-port RAM comes in many configurations, providing access to a shared memory space via plural input and output ports. Increasingly common is the ability to write plural data to the device simultaneously via separate ports. When data is written simultaneously to the same location from two-or-more ports, the integrity of the data is not guaranteed. The addressed memory location might contain new data, old data, or some transitional value. To mitigate this problem, additional logic is required to implement arbitration. Arbitration is coordinating by the processors access to memory locations.
Some digital computing system applications, for example, vital and mission critical systems require a high degree of safety. For example, for safe operation, an aircraft flight control computer depends upon continuous error-free computing operation for the entire period of flight. It should be recognized that error-free operation requires the elimination of, or containment of faults within the digital computing system. In addition to ever-increasing demands of reliability, a fast computing system with increased throughput is necessary for flight control and other vital systems.
To provide data integrity, more than one processor determines whether discrepancy exists in the information being simultaneously transferred over a bus. This comparison of data for highly accurate results is often referred to as “cross compare”. For example, by cross comparing computational results produced by different processors, high integrity of data is provided.
Current cross compare systems running in a multiprocessor configuration are slow, software intensive or complicated to setup. There are several solutions currently available. One solution used for dual systems requires either a parallel or serial port connection. Both parallel port and serial port solutions support only a limited amount of data that can be transferred at one time. The serial port based solution is slow and software intensive. The parallel port solution becomes slow whenever large amounts of data need to be cross compared.
Another solution is for triplicated systems using either a complicated hardware setup or a high speed serial connection which is software intensive and uses external wiring. When implemented using external, rack-based hardware, setup was complicated and hardware intensive. When implemented with high-speed serial communication (Ethernet), the arrangement was software intensive and speed limited by the external wiring.
As an example of a related art system, U.S. Pat. No. 6,182,196 discloses a method and apparatus for arbitrating access requests to a memory. The memory comprises a cross check module (502) comparing the client operation requests. When the cross check module (502) determines that the requests are contemporaneously attempting to access an identical memory block of memory, the cross check (502) arbitrates between the client operation requests. The arbitration is based on an arbitration rule and produces a first memory access request and a second memory access request.
As a further example of a prior system, U.S. Patent Application Publication 2002/0010902 discloses field programmable gate arrays (FPGAs) comprising embedded block RAM (EBR). In an embodiment, the EBR are multi-port RAM blocks embedded in a FPGA core. The EBR is used to increase the amount of memory and to complement distributed Programmable Function Unit memory. Arbitration is provided between write ports, and an arbitration unit receives memory request signals and selects a winner from among the requests.